The goal of this proposal is to develop a new genetic system that will mimic the natural process of evolution for a selected subset of genes inside of a bacterial cell. Instead of an evolutionary time scale of years, evolution will proceed at an accelerated rate and data will be collected in a matter of days. In addition to providing a powerful system to study evolution in the laboratory, such a system will form the core of a directed evolution technology. Directed evolution is an approach that enables scientists to "tune" the properties of enzymes for specific applications. Its benefit has become so apparent that today most new enzymes undergo some type of directed evolution before being commercialized. However, all current implementations of directed evolution are conducted step-wise, with each step in the evolution process necessitating a substantial amount of time and manpower. A single cycle of evolution usually takes a few days and involves demanding technical work at each step. Because enzymes usually need to undergo many cycles of evolution, each application can take a substantial amount of time. This proposal will yield a continuous in vivo directed evolution platform requiring only minimal external input. Such an evolution platform will enable scientists to conduct more than 20 cycles of evolution in the course of a single day. It thus has the potential to be 10X faster than current evolution technologies, 10X cheaper, easier to implement, and yield proteins that will theoretically be better optimized than those produced today. Such a system will enable the optimization of proteins for various industrial applications (catalysts for pharmaceutical chemical synthesis is one example), but more importantly, it will be adapted to mammalian systems to enable the in vivo evolution of peptide-based therapeutics (such as antibodies, cyclic peptides, and enzymes). These therapeutics will address critical areas such as antiviral and antimicrobial drugs.